The present application Inhibition of nNOS-PSD95 interactions: A novel approach to developing treatments for PTSD addresses the critical need for efficacious treatments for posttraumatic stress disorder (PTSD). A key neural signaling cascade activated by a trauma experience is initiated by the excitatory neurotransmitter glutamate. Activation of the NMDA receptor, a glutamate receptor subtype, results in subsequent activation of the enzyme neuronal nitric oxide synthase (nNOS) and, ultimately, an increase in the production of the signaling molecule nitric oxide (NO). These events trigger aberrant synaptic plasticity that is implicated in the initiation and maintenance of PTSD. Postsynaptic density protein 95 (PSD95) targets nNOS to the NMDA receptor and is, therefore, required for NMDA receptor activation of nNOS. Our group first showed that the small molecule inhibitor IC87201 disrupts the functional protein-protein interaction between nNOS and PSD95 in vitro and attenuates NMDA receptor dependent hyperalgesia in vivo. We have now shown that IC87201 and a related analog, ZL006, block the long-term encoding of conditioned fear even after a fear conditioning session has occurred (i.e. post-trauma). Unlike NMDA receptor antagonists, these protein interaction inhibitors are efficacious without impairing motor movement or memory. Thus, disruption of signal compartmentalization represents an innovative approach to develop novel treatments for anxiety disorders with fewer side-effects. We have assembled a collaborative team to conduct work proposed under two Specific Aims. Aim 1 will test the benefits of inhibiting nNOS-PSD95 interactions in preclinical models of PTSD symptoms. Aim 2 will study the neural substrate mediating effects of nNOS-PSD95 protein-protein interaction inhibitors on conditioned fear. Results from this study will lay the foundation for preclinical development of nNOS targeting inhibitors as novel treatments for PTSD. These studies are expected to validate the disruption of signal protein compartmentalization as an innovative and feasible approach to drug development. The development of effective pharmacotherapies with novel chemical structures that possess limited side-effect profiles is expected to drive down escalating health care costs and alleviate unnecessary suffering in PTSD patients.